High rates of cesarean delivery in the United States are a cause of urgent concern as cesarean delivery is associated with increased risks for maternal morbidity and mortality. Women with a first cesarean are at increased risk for serious complications such as uterine rupture, unplanned hysterectomy, and endometritis. The risk of severe maternal morbidity and poor neonatal outcomes increases with each subsequent cesarean delivery. The rise in cesarean delivery rates during the past two decades is a suspected driver of overall increases in maternal mortality and morbidity in the same time period. To reduce cesarean delivery rates among first-time mothers with low-risk pregnancies, the Health Resources and Services Administration is currently supporting implementation of a ?patient safety bundle? through state perinatal collaboratives. The proposed study will leverage a real world implementation of the cesarean bundle through the Maryland Perinatal Collaborative (MPC), which is one of the first state collaboratives to implement the bundle and includes 31 of the state?s 32 birthing hospitals. Our research team, with expertise in implementation science, obstetric care quality, and mixed-methods and qualitative research, will conduct a mixed-methods case study of bundle implementation at hospitals participating in the MPC. The proposed research will be the first implementation study of the cesarean bundle, and will address important gaps in the literature on guideline implementation in obstetric care. For our first aim, we will conduct qualitative interviews with MPC leaders and stakeholders to describe and categorize each hospital?s implementation approach and to identify barriers and facilitators for implementing the bundle. Interviews will address the five domains of the Consolidated Framework for Implementation Research (CFIR), and will contribute to building the evidence base for guideline implementation in obstetric care. Under our second aim, we will conduct Comparative Qualitative Analysis to assess which implementation factors are common to hospitals with high adoption of the bundle (>70% of bundle practices) and low adoption (<40% of practices), and hospitals with higher cesarean rates (>30 per 100 live births) and lower rates (<20 per 100). For our third aim, we will assess the maintenance of bundle EBPs, and any new adoption of EBPS, through a survey of MPC leaders one year after the collaborative ends. The results of this study will contribute to the development of an R01 proposal to test an implementation support package designed to improve implementation of the bundle and reduce cesarean delivery rates.